1. Field of Invention
The present invention relates to extrafine-strand-adaptable pressure contact blades which can be contacted by a wire including a core composed of extrafine strands.
2. Description of Related Art
The upper and lower limits of the settable range C (see FIG. 8) of the slot width of a slot to be formed by pressure contact blades are determined according to the following conditions. Here, FIG. 8 is a graphical representation of the relationship of the slot width with respect to the contact resistance and contact load between the pressure contact blades and the core of a wire. In FIG. 8, a graph A shows the relationship between the slot width and contact loads, whereas a graph B shows the relationship between the slot width and contact resistance. By the way, the relationships shown by the graphs A and B are based on test results obtained by conducting a pressure contact test repeatedly in which a wire is pressure contacted with the slot of the pressure contact blades, contact resistance and contact load between the core and pressure contact blades are measured, and the strands of a wire to be tested is checked for cutting.
The graph B shows that the contact resistance can provide a stable value in the vicinity of the minimum value when the slot width is within a given area. The upper limit of the settable range C of the slot width can be given in the following manner: in case where the slot width increases and thus the contact load decreases, at a certain value of the slot width, the contact resistance is thereby allowed to rise from a value in the vicinity of the minimum value thereof; that is, the upper limit can be given by such certain value of the slot width. Also, the lower limit of the settable range C of the slot width can be given in the following manner: in case where the slot width decreases down to such a value where one or more of the strands of the core is (or are) cut (cutting of strand), the contact load is thereby decreased, which in turn allows the contact resistance to rise from a value in the vicinity of the minimum value thereof; that is, the lower limit can be given by such value of the slot width.
Next, with reference to FIG. 9, description will be given below of how the settable range C varies when the section size of a core (core size) of a wire to be pressure contacted with the pressure contact blades is varied. By the way, three sets of graphs A1-A3, B1-B3 and settable ranges C1-C3 shown in FIG. 9 correspond to the above-mentioned graphs A, B and settable range C shown in FIG. 8 when the core size is varied in three stages. In the three sets of graphs A1-A3, B1-B3 and settable ranges C1-C3, the core size of the core increases sequentially in order from the left set to the right set.
Also, referring to the upper limit of the settable range C, in case where the core size decreases, the area (contact area) of the core where the core receives the contact load from the pressure contact blades also decreases and thus the contact load to be received by the core decreases, with the result that the upper limit of the settable range C is reduced accordingly. Also, in the case of the lower limit of the settable range C, in case where the core size decreases, the section size of strands (strand size) forming the core decreases accordingly, with the result that the cutting of the strands is easy to occur and the contact load is kept from increasing: that is, the lower limit of the settable range C increases as the core size decreases.
Therefore, as can also be seen from the results of a pressure contact test shown in FIG. 9, as the core size decreases, the settable range C of the slot width decreases.
On the other hand, even in case where a pressure contact terminal is manufactured in such a manner that the slot width provides a given set value Wa (see FIG. 10) present within the settable range C, due to the manufacturing tolerance D, the slot width of an actual product provides any one of values within a tolerance range E deviated by xc2x1D from the set value Wa.
Therefore, in case where the settable range C is too narrow, as shown in FIG. 10, the tolerance range E becomes larger than the settable range C and thus there is a fear that, when products are actually manufactured, some of them can have the slot width out of the settable range C.
Now, FIG. 11 is a perspective view of a pressure contact blade of an ordinary pressure contact terminal according to the related art. Right and left pressure contact blades 5 shown in FIG. 11 are formed integral with the pressure contact terminal in such a manner that they are formed by a pulling/raising operation so as to project inwardly from the right and left side walls 9 of the pressure contact terminal; and, the mutually opposed, vertically extending inner side end faces 5a of the two pressure contact blades 5 cooperate together in defining a slot 3.
However, when the thus structured conventional pressure contact blades 5 are applied to the pressure contact of a core composed of a bundle of seven or more strands and having a section size of 0.20 mm2 according to the invention (such core is composed of extrafine strands), there are found the following problems.
That is, in the conventional pressure contact blade 5, for example, in the case of the pressure contact blade 5 having a plate thickness T (see FIG. 11) of 0.25 mm, when the pressure contact blade 5 is applied to the pressure contact of a wire including a core having a section size of 0.13 mm2, the settable range C of the slot width obtained by a pressure contact test similar to the previously-described graphs A, B shown in FIG. 8 is given as 0.05 mm. On the other hand, in this application, a manufacturing tolerance D is 0.03 and a tolerance range E is 0.06 mm; that is, the tolerance range E is larger than the settable range C, which provides a poor yield rate and makes it substantially difficult to manufacture the pressure contact blade.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional pressure contact blade. Accordingly, it is an object of the invention to provide extrafine-strand-adaptable pressure contact blades which can set a slot width settable range to be determined by a pressure contact test larger than a tolerance range given by a manufacturing tolerance and can be manufactured easily.
In attaining the above object, according to the invention, there are provided extrafine-strand-adaptable pressure contact blades formed on a pressure contact terminal and including a slot to be pressure contactable by a wire including a core composed of a bundle of seven or more strands and having a core section size of 0.20 mm2, wherein the pressure contact blades are formed by blanking parts of the two mutually opposed right and left side wall portions of the pressure contact terminal so as to project inwardly in part; and also wherein, based on test results obtained by repetitively conducting a pressure contact test in which the wire including the core is pressure contacted with the slot, the contact resistance and contact load between the core and contact pressure blades are measured and the strands of the wire are checked for cutting while varying the slot width of the slot, of the varying ranges of the slot width and contact load, a range where the contact resistance is stable and the strand cutting of the wire cannot occur is defined as a slot width settable range and the range of a tolerance with respect to the slot width caused in the manufacture of the pressure contact terminal is defined as a tolerance range, and the whole contact area of the right and left side surfaces of the slot, which hold the core of the wire between them, with respect to the core is set in such a manner that the slot width settable range is larger than the tolerance range.
Preferably, the contact area may be set equal to or larger than 0.15 mm2.